1. Field
An apparatus and method for driving an LCD device is provided.
2. Related Art
Generally, LCDs adjust light transmittance of liquid crystal cells according to a video signal so as to display an image. An active matrix type LCD device has a switching element formed with every liquid crystal cell and is suitable for the display of a moving image. A thin film transistor (TFT) is mainly used as the switching element of the active matrix type LCD device.
FIG. 1 illustrates a related art apparatus for driving an LCD device.
Referring to FIG. 1, the related art apparatus for driving an LCD device includes an image display unit 2 including liquid crystal cells formed in each region defined by first to n-th gate lines GL1 to GLn and first to m-th data lines DL1 to DLm. A data driver 4 supplies analog video signals to the data lines DL1 to DLm. A gate driver 6 supplies scan signals to the gate lines GL1 to GLn. A timing controller 8 aligns externally input data RGB and supplies them to the data driver 4, generates data control signals DCS to control the data driver 4, and generates gate control signals GCS to control the gate driver 6.
The image display unit 2 includes a transistor array substrate, a color filter array substrate, a spacer, and a liquid crystal. The transistor array substrate and the color filter array substrate face each other and are bonded to each other. The spacer uniformly maintains a cell gap between the two substrates. The liquid crystal is filled in a liquid crystal area prepared by the spacer.
The image display unit 2 includes a TFT formed in the region defined by the gate lines GL1 to GLn and the data lines DL1 to DLm. The liquid crystal cells connect to the TFT. The TFT supplies the analog video signals from the data lines DL1 to DLm to the liquid crystal cells in response to the scan signals from the gate lines GL1 to GLn. The liquid crystal cell is comprised of common electrodes facing each other by interposing the liquid crystal therebetween and pixel electrodes connected to the TFT. Therefore, the liquid crystal cell is equivalent to a liquid crystal capacitor Clc. The liquid crystal cell includes a storage capacitor Cst connected to a previous gate line to maintain the analog video signals filled in the liquid crystal capacitor Clc until the next analog video signals are filled therein.
The timing controller 8 aligns the externally input data RGB to drive the image display unit 2 and supplies the aligned data to the data driver 4. Also, the timing controller 8 generates the data control signals DCS and the gate control signals GCS using a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronizing signals Hsync and Vsync, which are externally input, so as to control each driving timing of the data driver 4 and the gate driver 6.
The gate driver 6 includes a shift register that sequentially generates scan signals, for example, gate high signals in response to a gate start pulse (GSP) and a gate shift clock (GSC) are among the gate control signals GCS from the timing controller 8. The gate driver 6 sequentially supplies the gate high signals to the gate lines GL of the image display unit 2 to turn on the TFT connected to the gate lines GL.
The data driver 4 converts the data signals Data aligned from the timing controller 8 into the analog video signals in response to the data control signals DCS supplied from the timing controller 8. The data driver supplies the analog video signals corresponding to one horizontal line per one horizontal period in which the scan signals are supplied into the gate lines GL to the data lines DL. In other words, the data driver 4 selects a gamma voltage having a predetermined level depending on a gray level value of the data signals Data and supplies the selected gamma voltage to the data lines DL1 to DLm. At this time, the data driver 4 inverses polarity of the analog video signals supplied to the data lines DL in response to a polarity control signal POL.
The related art apparatus for driving an LCD device has a relatively slow response speed due to characteristics such as the inherent viscosity and elasticity of the liquid crystal. In other words, although the response speed of the liquid crystal may be different according to the physical properties and cell gap of the liquid crystal, it is common that the rising time is in the range of 20 ms to 80 ms and the falling time is in the range of 20 to 30 ms. Because this response speed is longer than one frame period (16.67 ms in National Television Standards Committee (NTSC)) of a moving image, as shown in FIG. 2, the response of the liquid crystal proceeds to the next frame before the voltage being charged on the liquid crystal cell reaches a desired level.
Since the image of each frame displayed in the image display unit 2 affects the image of the next frame, motion blurring occurs in the moving image due to perception of a viewer.
In the related art apparatus and method for driving an LCD device, motion blurring causes degradation in contrast ratio, and, in turn, degradation in display quality.
In order to prevent motion blurring from occurring, an over-driving apparatus has been suggested that modulates a data signal to obtain the fast response speed of the liquid crystal.
FIG. 3 is a block diagram illustrating a related art over-driving apparatus.
Referring to FIG. 3, the related art over-driving apparatus 50 includes a frame memory 52 that stores RGB data of a current frame Fn. A look-up table 54 generates modulated data that obtains the fast response speed of the liquid crystal by comparing the data RGB of the current frame Fn with data of a previous frame Fn-1 stored in the frame memory 52. A mixing unit 56 mixes the modulated data from the look-up table 54 with the data RGB of the current frame Fn.
The look-up table 54 lists modulated data R′G′B′ that converts a voltage of the data RGB of the current frame Fn into a higher voltage to obtain the fast response speed of the liquid crystal, thereby adapting to a gray level value of an image moving at the fast speed.
In the aforementioned related art over-driving apparatus 50, since a voltage higher than an actual data voltage is applied to the liquid crystal using the look-up table 54 as shown in FIG. 4, the fast response speed of the liquid crystal is adapted to a target gray level voltage until a desired gray level value is actually obtained.
The related art over-driving apparatus 50 can reduce motion blurring of a display image by accelerating the response speed of the liquid crystal using the modulated data R′G′B′.
A problem occurs in that the related art because the LCD device fails to obtain a clear image due to motion blurring occurring in boundaries A and B of each image, as shown in FIG. 5, even though the image is displayed using the over-driving apparatus. In other words, since luminance increases between the boundaries A and B of the image to have a tilt, motion blurring still occurs even though the liquid crystal is driven at a high speed.
If the display image is driven in a frame frequency of 120 Hz, the related art LCD device can reduce motion blurring of the display image. However, there may exist various problems relating to the charge and discharge of the image display unit, a thermal problem of a driver, electromagnetic interference (EMI) caused by high frequency, and difficulty in a circuit design.